I can only find one post on the entire internet with the same problem as this, so I doubt i'm going to get flooded with answers but basically i'm trying to upgrade a Yosemite Mac mini to El Capitan which is running a DIY Fusion drive.
Its made up of an internal SSD and an external Thunderbolt G-Raid Raid Array (2x 4tb WD Red's) to great an 8.25TB Corestorage volume.
The problem is when I try to upgrade to El Cap i get the error message
"OS X Could not be installed on your computer. A partition, not a whole disk is required for this operation".
I can't even think what its referring to, the fusion drive seems to follow Apple's conventions. It was missing a recovery HD which is the only thing I thought could be an issue so I recreated that, but no luck, still got the same error message.
Anyone suggest anything?